Autothermal and partial oxidation reformer-based fuel processor, method for improving catalyst function in autothermal and partial oxidation reformer-based processors

ABSTRACT

The invention provides a fuel processor comprising a linear flow structure having an upstream portion and a downstream portion; a first catalyst supported at the upstream portion; and a second catalyst supported at the downstream portion, wherein the first catalyst is in fluid communication with the second catalyst. Also provided is a method for reforming fuel, the method comprising contacting the fuel to an oxidation catalyst so as to partially oxidize the fuel and generate heat; warming incoming fuel with the heat while simultaneously warming a reforming catalyst with the heat; and reacting the partially oxidized fuel with steam using the reforming catalyst.

PRIORITY

This Utility Patent Application claims the benefits of U.S. ProvisionalPatent Application No. 61/106,888, filed on Oct. 20, 2008.

CONTRACTUAL ORIGIN OF THE INVENTION

The U.S. Government has rights in this invention pursuant to ContractNo. DE-AC02-06CH11357 between the U.S. Department of Energy and theUniversity of Chicago representing Argonne National Laboratory.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to partial oxidation or autothermalreforming of fuel, and more specifically, the invention relates tosegmented catalyst systems for use in reforming of fuel for use in fuelcells.

2. Background of the Invention

Partial oxidation and autothermal reformers convert hydrocarbon andoxygenated fuels into hydrogen and carbon oxides which can be used infuel cell applications; particularly fuel cell applications constrainedby weight and volume, or which require frequent starts and stops, andhave to respond to changes in hydrogen demand. Partial oxidation andautothermal reformers are able to meet these requirements because thesereactors operate with a feed that consists of fuel and air in partialoxidation systems and fuel, air and steam in autothermal reformers.Oxygen in the reactant mix allows the fuel oxidation/combustionreaction, which is needed to enable the endothermic steam reformingreaction to occur.

The reforming reactors typically use a noble metal catalyst thatsupports both the oxidation and reforming reactions, with the oxidationzone followed by the reforming zone. The Reforming zone is where oxygenconcentration is extremely low.

Generally, a partial oxidation/combustion reaction first occurs asdepicted in Equation 1:

C_(n)H_(m)+O₂→CO+CO₂+H₂O.  Equation 1

The reaction in Equation 1 is exothermic and provides heat necessary todrive the reforming portion of any autothermal reformer system, thereforming portion depicted in Equation 2:

C_(n)H_(m)+H₂O→CO+CO₂+H₂  Equation 2

Generally, the reforming portion (i.e., Equation 2) of the processoccurs at relatively low oxygen concentrations.

Temperature profiles consist of a sharp peak that can reach or exceed1000° C., at which temperature the catalyst activity diminishes overtime. In order to reduce the maximum temperature and thereby extend thelife of the catalyst, reactor designs vary the air-to-fuel, allowmultiple injections of air, and, in the case of autothermal reformers,steam-to-fuel ratios. While reducing the air in the mixture feeds (i.e.,making the fuel mix richer) will minimize peak temperatures, it alsoleads to a lower average temperature and therefore to lower hydrogenyields.

Other attempts to lower system temperature include siphoning heat fromexothermic portions of the reaction, warming air with that heat, theninjecting that heated air at multiple injection points. However, thishas proved counterproductive, inasmuch as the air reacts with anyhydrogen produced instead of being utilized to facilitate oxidation ofthe carbon in the unconverted hydrocarbon.

A need exists in the art for a system for reforming fuel, and a methodfor reforming fuel that preserves the life of the catalysts used in suchscenarios. The method and system should provide for near completeconversion of fuel, while also ensuring that the catalysts last for atleast 5000 start-stop cycles, assuming 10 hours per cycle. The methodand system should also be initiated with an energy input (in BTUs) whichis no more than 1 to 3 percent, and preferably less than one percent ofthe total energy produced by the system/method during each cycle.

SUMMARY OF INVENTION

An object of the invention is to provide a method for improving catalystfunction in autothermal and partial oxidation reformer-based processorsthat overcomes many of the disadvantages of the prior art.

Another object of the present invention is to provide a system forvastly increasing the catalyst life in autothermal and partial oxidationreformer-based processors. A feature of the invention is the physicalseparation of different catalysts in the system. An advantage of theinvention is that the different catalysts are each heated to theiroptimum operating temperature to concomitantly facilitate chemicalconversions.

Yet another object of the present invention is to provide a partialoxidation or an autothermal reformer based system which comprises threetemperature zones. A feature of the invention is a porous catalystsupport structure that extends throughout the zones, such that catalystsused in the system all contact the structure so as to be supported bythe structure. An advantage of the invention is that the structureprovides a conduit for both heat and fluids to traverse through thezones, thereby establishing fluid communication between the temperaturezones. This structure provides a means for dissipating thermal energygenerated in oxygen-rich upstream conversions so as to protect more heatsensitive, downstream noble-metal catalysts.

Briefly, the invention provides a fuel processor comprising a linearflow structure having an upstream portion and a downstream portion; afirst catalyst supported at the upstream portion; and a second catalystsupported at the downstream portion, wherein the first catalyst is influid communication with the second catalyst.

Also provided is a method for reforming fuel, the method comprising:contacting the fuel to an oxidation catalyst so as to partially oxidizethe fuel and generate heat; warming incoming fuel with the heat whilesimultaneously warming a reforming catalyst with the heat; and reactingthe partially oxidized fuel with steam in the presence of the reformingcatalyst.

BRIEF DESCRIPTION OF DRAWING

The invention together with the above and other objects and advantageswill be best understood from the following detailed description of thepreferred embodiment of the invention shown in the accompanyingdrawings, wherein:

FIGS. 1A-B are schematic drawings of a catalyst system encapsulated by ahousing, in accordance with features of the present invention;

FIG. 2 is graph showing temperature profiles for catalysts in the systemfor three different ignition scenarios, for a three region reactor inaccordance with features of the present invention;

FIG. 3 is a graph showing temperature profiles for catalysts in a tworegion reactor, in accordance with features of the present invention;

FIG. 4 is a graph showing temperature profiles at an oxygen/carbon ratioof 0.53 and a steam to carbon ratio of 2;

FIG. 5 is a schematic diagram showing the segmented catalyst inoperation, in accordance with features of the present invention,

FIG. 6A is a graph of temperature profiles in the ATR, as a function oftime, in accordance with features of the present invention;

FIG. 6B is a chart showing product yields in various portions of theATR, in accordance with features of the present invention;

FIG. 7 is a graph showing light off temperatures as a function of fuelflow rates, in accordance with features of the present invention;

FIG. 8 is a series of graphs showing light off temperatures as afunction of the slope of exit surface catalyst temperatures/inletsurface catalyst temperatures, in accordance with features of thepresent invention;

FIG. 9 depicts a plot of the inlet feed temperature to thehexa-aluminate at the point of ignition as function of flow rate, inaccordance with features of the present invention;

FIG. 10 is a graph showing the ignition temperature as a function of airto carbon ratio, in accordance with features of the present invention;and

FIG. 11 is a graph showing the ignition temperature as a function ofsteam to carbon ratio, in accordance with features of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing summary, as well as the following detailed description ofcertain embodiments of the present invention, will be better understoodwhen read in conjunction with the appended drawings.

As used herein, an element or step recited in the singular and precededwith the word “a” or “an” should be understood as not excluding pluralsaid elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features. Moreover, unlessexplicitly stated to the contrary, embodiments “comprising” or “having”an element or a plurality of elements having a particular property mayinclude additional such elements not having that property.

The invention is a process and new reactor design that overcomes theproblem of catalyst durability resulting from the high temperaturesencountered in autothermal and partial oxidation reactors, yet hasexcellent durability and is of simple design. The system allows theoxidation reactions (i.e. “light off”) to begin as low as about 480 C inthe presence of oxygen.

An embodiment of the new reactor design embodies a two step system, witheach step associated with a catalyst. One of the catalysts (the moreupstream of the two catalysts) is a high (i.e. above 900 C) temperaturecatalyst (such as hexa-aluminate) while the other catalyst is arelatively lower temperature (i.e., below 900 C) catalyst (such as anoble metal catalyst).

Another embodiment of the invention embodies three conductive catalystsupport structures or units. The first structure provides a means fordistributing the feed radially and to heat incoming reactant stream.This means includes, but is not limited to, a metallic foam whichfacilitates fluid transfer in all directions of the foam. This foam,positioned before (or upstream of) the first active catalyst, disperses(by conduction) the heat of reaction of the exothermic process on thefirst active catalyst, toward the incoming feed stream (counter-currentto the direction of flow and preheating the incoming feed). Thisflattens out the axial temperature profile of the reactor, therebyreducing peak temperatures experienced by catalysts which facilitateendothermic steam reforming reactions. This transfer of heat upstreamprovides a means for limiting the peak temperature experienced by thetemperature-sensitive downstream catalysts.

The second unit is a support (which could be contiguous with themetallic foam structure) loaded with an oxidation catalyst (e.g., withhexa-aluminate, (ABAl₁₁O₁₉)) to promote the rapid oxidation/combustionreaction. These oxidation reactions generate sufficient temperaturessuch that the steam reforming reaction can occur on the hexa-aluminatecatalysts and in the gas phase homogeneously. The third unit is loadedwith a reformer catalyst such as noble metal catalyst.

Generally, all that is required in the positioning of these catalysts isthat fluid communication exists between the catalysts. As such, a singlecatalyst support substrate defining flow through conduits from itsupstream end to its downstream end is suitable, wherein zones of thesupport are devoted to supporting only specific catalyst types. Thisfeature provides a means for rapid dissipation of heat from exothermiccatalysts toward the cooler, feed inlet, and also simultaneously towardthe reforming, endothermic reaction facilitating catalyst downstream. Assuch, this feature provides a means for anchoring the process's peaktemperature within the upstream, exothermic reaction facilitatingcatalyst, where the reactant mix is richer in oxygen.

Conversely, a plurality of support substrates, each supporting aspecific catalyst is suitable, wherein the support substrates arepositioned end-to-end to facilitate fluid flow through from an upstream(or fuel ingress) end of the system to the downstream or egress end ofthe system.

Compared to the noble metal catalyst, the oxidation/combustion catalystshave lower activity, i.e., slower reaction rate at a given temperature,and can tolerate higher temperatures. For example, as an embodiment ofan oxidation catalyst, hexa-aluminate can be supported on a poroussupport with high thermal conductivity, such as a metallic foam, toenable rapid dissipation of heat toward the cooler feed inlet and thereforming catalyst downstream.

Benefits of this design are that the peak temperature is sequestered orotherwise contained within the support substrate supporting theoxidation catalyst (e.g. hexa-aluminate), which can tolerate the hightemperature, while reducing the peak temperature in the noble metal.During start-up, the up stream catalyst needs to be heated to a highertemperature (compared to the noble metal catalyst) before “ignition” cantake place. This can be overcome by heating the hexa-aluminate zone tothe higher ignition temperature (higher relative to the light offtemperature needed by the downstream reforming catalyst) with a hotterfeed stream of gases, spark plugs, or with electric heating elementsthat can be turned off after ignition.

Foundation Substrate Detail

FIG. 1 depicts an exemplary segmented catalyst system, designated asnumeral 10. A salient feature of the system is a catalyst supportsubstrate 12. This support 12 comprises a heat resistant material(resistant to at least 1400° C.) which has an extremely high surfacearea. The substrate can be either one piece, as depicted, or a pluralityof pieces. Exemplary surface areas range from about 1 m²/g to 1200 m²/g,preferably from about 1 m²/g to 120 m²/g.

Suitable support substrate material includes, but is not limited toCordierite, Alumina, Mullite, Lithium aluminum silicate, and Aluminumtitanate. These materials have maximum temperatures ranging from 1300°C. for the lithium material to 1800° C. for the alumina. Commerciallyavailable cordierite monolith is available from Corning. Metallic foam,such as iron chromium aluminum alloy (FeCrAlY), is available fromPorvair (Norfolk, UK).

Whatever catalyst support substrate is utilized, it is preferable thatthe support enable fluid transfer from one end to another in a fashionto maximize catalytic interaction between the fluid and the catalystsresiding on the support. One means for enabling fluid transfer is wherethe support defines conduits, channels or other passageways 22throughout its bulk.

As depicted in FIG. 1A, a housing, 11, reminiscent of a sleeve,encapsulates peripheral regions of the support 12 and longitudinally(i.e., axially) extends along substantially the entire length of theconfiguration so as to encircle peripheral regions of all of thecatalysts utilized. In one embodiment, an upstream (i.e., proximal) end11 p of the housing is wider, in flow through diameter, than adownstream (i.e. distal) end 11 d of the housing 11.

The housing 11 also may resemble a sleeve having a first feed inlet end,a second, product exit end, and a midsection which has a diameter largerthan the first and/or second end. One embodiment of this housing isdepicted in FIG. 1B, and comprises a sphere (having a diameter d)positioned between two co-axial cylinders (each having an innerdiameter<d). All of the volume defined by the cylinders and most of thevolume defined by the sphere provides a linear flow passage or conduitin which are situated the catalysts. However, and as FIG. 1B depicts,this embodiment provides laterally spaced regions of the catalysts,positioned within the midsection of the housing, which remain outside ofdirect fluid flow.

Oxidation Region Detail

FIG. 1A depicts arrows which show the direction of fluid flow throughthe system. The upstream portion 14 of the system supports a catalyst tofacilitate the reactions depicted in Equation 1, supra. As such,catalysts which can withstand temperatures up to their sintering point(e.g., 1200° C. for hexa-aluminate) are suitable. Suitable catalysts forthis oxidation portion of the system are those which have enhancedoxygenation activities at temperatures above 900 C, preferably betweenabout 900 C and 1200 C, and most preferably between about 900 C and 1000C. A salient feature of the device is to facilitate conversion ofhydrocarbon or oxygenated hydrocarbon fractions to hydrogen and carbonoxide gases at as low a temperature as possible. This will obviate theneed for large quantities of more expensive finisher catalysts, such asthose containing noble metals.

Exemplary catalysts for the oxidation portion of the system include, butare not limited to, hexyluminates, spinels, perovskites, and garnets.Specific suitable hexa aluminates include, but are not limited to,LaAl₁₁O₁₉, LaMnAl₁₁O₁₂. Suitable spinels include, but are not limitedto, MgAl₂O₄, MgMn_(0.25)Al_(1.75)O₄. Suitable garnets include, but arenot limited to, Y₃Al₅O₁₂ and Y₃Mn_(0.1)Al_(4.9)O₁₂6Al₂O₃. Suitablepervoskites include, but are not limited to, LaMnO₃, LaCoO₃. Generally,these oxidation/combustion catalysts have lower activity and toleratehigher temperatures. Therefore, they are utilized in the hottest,upstream portions of the system.

Reformer Region Detail

The downstream portion 16 of the system supports a finisher catalyst tofacilitate the reactions depicted in Equation 2, supra. Generally, suchreforming catalysts provide optimal performances at temperatures notexceeding 850° C. Also, this portion of the system must operate at lowoxygen concentrations to avoid rapid oxidation reactions that willproduce hotspots on the catalyst surface leading to deactivation.Typical mole fractions for oxygen in the reaction fluid should rangefrom between about 0 and 5 percent, preferably from about 0 to 1percent, and most preferably from about 0 to 0.5 percent.

Preferably, support foundation substrates for the catalysts and catalystsupports in this region of the system are of the relatively lowerthermal conductivity variety (such as ceramic foam) so as to conserveany heat directed to it from the upstream oxidation process. Exemplarycatalysts for this portion of the system include, but are not limited tocatalysts containing such noble metals as Rh, Pt, Pd, or metals/metaloxides Ni, Co, NiO, and combinations thereof. Supports for these noblemetals include La—Al₂O₃, hexa-aluminate structures, TiO₂, La₂O₃, CeO₂,Gd—CeO₂, ZrO₂, MgO, SiO₂ γ-Al₂O₃, Y₂O₃ and combinations thereof. Thesenoble metal supports in turn, rest upon the foundation substrates (i.e.the catalyst support substrates) discussed supra.

Rhodium-based catalysts are particularly suitable inasmuch as rhodiumhas very high activity and selectivity for H₂ and CO. Rhodium alsodisplays a lower tendency to coke. When rhodium is loaded on La—Al₂O₃supports (which has a surface area greater than 90 m²/g) the rhodiummaintains a high dispersion at 900° C. Preferable reformationtemperatures are 750-850° C.

Preheater Portion Detail

Attention is directed now to the leading edge 19 of the catalyst support12. The support defines a larger diameter at this region of the system,compared to further downstream. This larger diameter provides a meansfor ensuring that any heat generated by the reactions furtherdownstream, is not immediately blown further downstream by the velocityof the reaction mixture. Rather, the leading edge 19 of the catalystsupport 12 remains uncoated so as to allow heat to travel in acountercurrent fashion so as to preheat incoming fuel.

FIG. 5 provides a schematic depiction of a feature of the inventionwhereby flame velocity (V_(f)) is generally greater than incoming fuelvelocity (V_(i)) so as to ensure preheating of the fuel prior to itsignition in the bulk of the oxidation catalyst support foundation. FIG.5 depicts the preheating zone 19 as comprising a metallic foam, whilethe oxidation 14 and reforming zones 16 are more linear-flow monolith(e.g. cordierite) in structure. FIG. 5 also depicts two differentfoundation substrates, axially aligned so as to facilitate fluid flowfrom the substrate supporting exothermic region 14 to the substratesupporting the reformer region 16. However, and as noted above, theexothermic region and the reformer region can be supported on onecontiguous foundation substrate 12 as depicted in FIG. 1.

Generally, and as noted supra, the front region of the system is definedby a metallic foam so as to assure radial dispersion of incoming fuel tothe entire diameter of the catalytic support structure, and also toassure blow back of heat, which is generated from the mid portion 21 ofthe exothermic reaction zone of the system, toward the fuel ingresspoint.

The high heat generated in the exothermic reactions (which are relegatedto the upstream portion 14 of the system) also dissipates toward thedownstream portion 16 of the system, thereby providing heat tofacilitate the endothermic process occurring there. Inasmuch as acertain amount of heat dissipation will occur from the exothermicreaction region of the system to all portions of the system, the heatradiating toward the downstream portion will be considerably less thanthe heat found in the exothermic region. This dissipation then, providesa means for isolating the more temperature intolerant reformingcatalysts from the high temperature regions of the system.

In summary of this point, the flow-through character of the catalyticsupport provides a means to simultaneously preheat incoming fuel, andprovide heat to the reforming reaction.

FIG. 2 depicts the effect of fuel conversion and catalyst temperaturefor three different cases. In case A, ignition of fuel and air occurs onthe hexa-aluminate (upstream portion 14). The temperature increasesrapidly due to the oxidation reaction. When oxygen has been consumed,the temperature progressively cools due to the endothermic reactions.After the hexa-aluminate, the temperature has dropped to 840° C. andapproximately 80 percent of the fuel has been converted.

Case B shows the scenario where ignition occurs on the Rh-catalystsection (i.e., the downstream portion 16). The exit conversion after theRh-catalyst is similar between case A and B, but the Rh-catalyst in caseB peaks at 970° C., which will damage the reforming catalyst.

In Case C, ignition occurs again on the Rh-catalyst section but theair-to-fuel ratio is decreased to 0.36 from 0.53 to reduce the peaktemperature. The peak temperature of 840° C. seen by the Rh catalyst isthe same as in Case A, but because of the lower average bed temperaturein Case C, the conversion of the fuel is much lower (80 percent comparedto 98.6 percent in Case A).

FIG. 2 also shows the three portions of the catalyst support, asdiscussed supra. Specifically, the uncoated portion 18 of the catalystis designated as “blank foam” in the figure. The oxidation or upstreamportion 14 of the catalyst support is designated as “hexa-aluminate.”The reforming or downstream portion 16 of the catalyst support isdesignated as “Rh/aluminate.” The blank foam region serves as a means todistribute the fuel feed radially and to heat incoming reactant stream.The hexa-aluminate region, positioned intermediate the blank foam andthe reforming region, promotes rapid oxidation/combustion reactions andgenerates sufficient temperatures to facilitate endothermic steamreformation in the Rh/aluminate portion of the system.

In an embodiment of the invention, palladium catalyst is applied nearthe leading edge 19 of the catalyst support. Such placement of anoxidation catalyst serves to initialize combustion anchor the flamefront at the proximal end of the system. This, further insulates themore sensitive reforming catalyst from heat spikes.

The three region system confers the following benefits:

1. Peak temperatures generated in the system are anchored within thehexa-aluminate catalyst where the reactant mix is richer in oxygen.

2. By flattening out the axial temperature profile in the reactor(including the maximum temperature in the noble metal), it offersgreater flexibility in the choice of operating parameters, e.g., ahigher air-to-fuel ratio.

3. The high temperatures in the hexa-aluminate unit support thereforming reaction both in the homogeneous (gas) phase and on thehexa-aluminate catalyst surface.

4. The metal foam support 12 dissipates the thermal energy to the inletzone, raising the temperature to initiate the oxidation reactions of themuch cooler reactant feed.

5. The metal foam support dissipates the thermal energy to the noblemetal catalyst to support the endothermic steam reforming reaction.

6. Uncoated foam is placed before (i.e., upstream of) the activecatalyst to disperse the heat of reaction and preheat the inlet gas,simultaneously.

7. The temperature profile within the autothermal reformer isconsiderably more damped, thereby reducing the thermal stress in thecatalyst.

8. The desired conversion of the fuel to the reformate gas is achievedwithin a smaller catalyst volume.

FIG. 3 depicts a two bed autothermal reactor. As depicted in FIGS. 2 and3, the volume of oxidation catalyst compared to noble metal catalyst isconsiderably less. For example, FIG. 2 shows the oxidation-to-reformercatalyst volume ratio of 1.5:6. FIG. 3 shows that the high temperatures(as high as 1075° C.) in the hexa-aluminate unit support the reformingreaction both in the homogeneous (gas) phase and on the hexa-aluminatecatalyst surface.

FIG. 4 shows a graph of oxidation/reforming temperatures related tomethane fuel, with an even lower oxygen/carbon ratio of 0.53 than the0.58 ratio of FIG. 3.

Operation Detail

The goal of the invented authothermal reformer (ATR) system is tooptimize hydrogen gas production at the lowest temperatures possible.The following example features a dual bed design comprising ahexa-aluminate upstream catalyst and an RH catalyst for the downstream,finishing catalyst. The example is provided for illustrative purposesonly, and is not to be construed as relegating the invention to thoseparticular catalysts.

Hexa-aluminate catalysts tolerate high temperatures but are less activeand need higher feed temperatures to ignite and sustain oxidationreactions. The ignition temperature, that is at what inlet feedtemperature oxygen is consumed within the hexa-aluminate catalyst, wasinvestigated and correlated as function of flow rate, O₂/C and S/Cratios. A higher inlet temperature is needed to initiate oxidationreactions in the hexa-aluminate catalyst by a) increasing the flow rateof the feedstream through the system, b) decreasing the oxygen to carbon(O2/C) ratio or c) increasing the steam to carbon (S/C) ratio.

A piece of uncoated foam, element 18 in FIG. 1 preceded the catalyst andserved to provide a uniform flow-rate to the catalyst section. A heatingcoil positioned proximal to (i.e., upstream from) the uncoated foamprovided additional heat to the inlet reactants, since thehexa-aluminate catalyst needs higher inlet temperatures than theRh-catalyst to sustain oxidation reactions.

The ATR catalyst was segmented into 3 sections; the first section was ahexa-aluminate catalyst (SrMnAlO) followed by the Rh-catalyst segments(Rh on La-stabilized alumina) segments. All catalysts were supported onmetal foams, FeCrAllY (40 ppi). There were two gas-sampling ports toanalyze the reformate composition, at the exit of the reactor andbetween the hexa-aluminate and the first Rh-segment.

Overall, it was found that at low inlet temperatures, the peaktemperature and oxygen consumption occurred at the front section of theRh-catalyst. As the inlet temperature increases, the oxygen is consumedon the hexa-aluminate catalyst with associated peaks in temperatureprogressing from the Rh-segment to the inlet face of the hexa-aluminate.

FIG. 6A shows an example of the temperature profiles and product yieldsbefore and after ignition in the hexa-aluminate catalyst for 70% ofrated flow (20 SLPM; SLPM=liters per minute at 25° C. and ambientpressure). The figure shows the temperatures at 5 axial locations. T-SMdenotes the temperature at the exit (centered) of the static mixer,T-BF₀ the temperature at the exit (centered) face of the uncoated foam(blank foam). T-HX₀ and T-HX_(e) denote the temperatures at the inletand exit face of the hexa-aluminate. T-Rh₀ is the temperature measuredat the inlet face of the first Rh-segment. The temperature in thecatalyst sections were evaluated at three locations in the radial planeand plotted as an arithmetic average value. When the inlet feedtemperature is low, the oxygen is primarily consumed up-stream theRh-catalyst with an associated maximum in temperature (peak). As seen inFIG. 6A, at a time of ˜50 min, the temperature at the front of the Rh isover 850° C. while the exit of the hexa-aluminate catalyst is about 650°C. The inlet temperature to the hexa-aluminate catalyst at that point is525° C.

As depicted in FIG. 6B, some oxygen, especially as the temperatureincreases, is consumed at the last stages of the hexa-aluminate volume.As seen in the measured product yield after the hexa-aluminate (20-30minutes), there is a decrease in O₂ and CH₄ yields and 0.25mol-H₂/mol-CH₄ is formed. This hydrogen production is the result of aconversion obtained within the hexa-aluminate, combined with somecontribution of the inlet face of the Rh-catalyst. Some fuel conversionoccurs at the last parts of the hexa-aluminate.

There is a substantial temperature increase at the exit of thehexa-aluminate due to back conduction from the Rh-catalyst. Astemperature increases, kinetics starts to increase and slowly consumemore fuel (and oxygen). The slope of the exit temperature of thehexa-aluminate catalyst is higher than the slope of the inlettemperature to this segment. Some heat release is occurring at the exitpart due to some O₂ consumption. As temperature is increased further,more O₂ is consumed, more heat is released and the reactionself-accelerates to the point where the temperature spikes at the exitof the hexa-aluminate. Just after 55 min, most (if not all of oxygen) isconsumed down-stream of the hexa-aluminate as the exit temperatureincreases rapidly and the temperature at the front of the Rh (T-Rh0)drops. The oxidation reaction progresses from the hexa-aluminate/Rhodiuminterfaces and at about 56 min, the oxygen consumption occurs at theinlet (front-face) of the hexa-aluminate catalyst. At that point, thepeak temperature is located at the front of the hexa-aluminate, almost900° C., and the temperature falls progressively downstream, with thegases finally entering the Rh-segment at 800° C.

At that point in time, all oxygen is consumed within the hexa-aluminate,as can be seen in FIG. 6B, between 60-75 min. A substantial amount of H₂is also formed (1.4 mol/mol-CH₄) and 0.3 mol/mol-CH₄ of CO and CO₂.Furthermore, some trace amount of ethane can be seen after thehexa-aluminate, something that is not observed after the Rh catalyst.

At equilibrium conditions (corresponding to the feed proportions used inthese tests), the predicted yields for H₂ and CO are ˜1.85 and ˜1.0mol/(mole-CH₄), respectively. The experimental conversion of methane, asseen in the figure, is not complete after the hexa-aluminate segment,the methane conversion is about 70%. The reforming reaction (steamreforming) appears to be slower within the hexa-aluminate layer;however, the gas hourly space velocity (GHSV) in this segment is closeto 100,000 h-1 while the GHSV of the Rh segments is 30,000 h⁻¹.

Analysis of the product yields after the ATR reactor (Rh catalyst)reveals that before the hexa-aluminate ignites, substantially all thefuel is consumed in the Rh catalyst. The product yields are shown inFIG. 6B in the time frame between 30 and 60 minutes. Once oxygen isentirely consumed within the hexa-aluminate catalyst, the yields afterthe ATR are shown in the time frame 75-90 minutes. The gas yields at theATR outlet are essentially the same. The difference is that once oxygenis consumed in the hexa-aluminate catalyst the Rh catalyst converts theunconverted fuel by steam-reforming reaction at substantially lowertemperatures (between about 750 and 800 C) than those temperaturespresent (at least 850) when oxygen was present in the Rh segment (30-60min).

Fuel Flow Detail

The ignition characteristics of the hexa-aluminate are effected by theflow-rate (or superficial velocity) of the fuel through this upstreamcatalyst. A higher velocity through the catalyst decreases the residencetime for the reaction to occur within the catalyst and also increasesthe cooling of the catalyst surface. Therefore, light-off temperaturesincrease as flow-rate increases. For this example, base case conditionsfor the light-off tests comprised an inlet feed of: O2/C=0.52 andS/C=1.65. At 100% rated power, the methane flow is 5.5 SLPM (total flowentering the catalyst is 28.19 SLPM).

As can be determined from FIG. 6A, when the inlet feed temperature ishigh enough, the temperature at the back end of the hexa-aluminatecatalyst increases sharply. Once this happens, the oxygen consumptionand, consequently temperature peak, progresses rapidly up-stream to theinlet part of the hexa-aluminate. Ignition, that is when oxidationreactions are sustained in the hexa-aluminate, is therefore defined asthe condition when the peak temperature moves from the noble metalcatalyst, upstream to the leading edge of the hexa-aluminate catalyst.

The inventors have determined that establishing low velocity within theupstream exothermic reaction facilitating catalyst (e.g., hexa-aluminatebased catalysts) allows hot zones, which developed in those catalysts,to travel backwards through the catalyst, and toward the fuel inlet ofthe system. This heat transfer upstream is found to be faster than theconvective cooling of the incoming reactants.

Low velocities are maintained by using a smaller length to diameterratio or using a variable diameter reactor (e.g., conically shaped) suchthat the reactor section encircling the partial oxidation catalyst(e.g., hexa-aluminate) closest to the fuel inlet has a larger diameterthan its downstream counterpart. In one embodiment of the invention, thecurrent length to diameter ratio for the downstream portion of thedevice is 1:1.5 or about 0.67. Therefore, a length to diameter ratio ofless than about 0.67 is suitable for the proximal end (i.e, the endadapted to receive unreacted fuel) of the device. Generally, in such anembodiment of the invention, the proximal end of the device defines alength to diameter ratio that is less than the length to diameter ratiodefined downstream by the housing of the device which encircles thenoble metal catalyst.

FIG. 6B reveals product yields during the above-described heatingprofiles. FIG. 6B comprises four panels. The first panel showsreactant/product mix for that portion of the system just downstream ofthe hexa-aluminate catalyst, and upstream from the noble metal catalyst.The second and fourth panel shows reactant and product mix which existsat that portion of the system which is directly downstream of thenoble-metal catalyst.

The feed temperature at ignition point is correlated by the temperaturemeasured at the front of the hexa-aluminate. FIG. 7 shows thetemperature at the exit section (T-HX_(e)) of the hexa-aluminatecatalyst as function of its inlet counterpart (T-HX₀) for threedifferent flow-rates. For each flow-rate, the inlet temperature (T-HX₀)is ramped up by turning on the heating coils located above the uncoatedfoam (see FIG. 1, element 18). The solid symbols denote the point ofignition, where the exit temperature (T-HX_(e)) sharply increases givena small increment of the inlet temperature (T-HX₀).

FIG. 7 clearly shows an increase in light off temperature withincreasing fuel flow rates.

Ignition Point as Function of Slope of T-Hx_(e)/T-Hx_(o)

The ignition point is evaluated according to the derivative of the exittemperature and inlet temperature (dT-HX_(e)/dT-HX₀) as shown below InFIG. 8. At the point of ignition, the derivative changes drastically andsignificantly increases from being almost zero before ignition. Todifferentiate the light-off point from the experimental data scattering,the light-off point is defined as when the derivative exceeds a value of5.

The base parameters which established this function are O₂/C of about0.52 and a S/C of about 1.65.

As discussed supra, the higher the flow-rate (velocity) of the fuelstream, the higher the inlet feed temperature needs to be in order tosustain the oxidation reactions within the hexa-aluminate section. Asflow increases, the residence time decreases for the oxidation reactionand more heat is transferred to the gas-phase removing heat from thecatalyst surface. Another effect of the cooling mechanism is that lessheat is transferred from the Rh-segment to the hexa-aluminate byback-conduction as the flow increases.

FIG. 9 depicts a plot of the inlet feed temperature to thehexa-aluminate at the point of ignition as function of flow rate. As theinlet flow doubles, the inlet feed temperature for ignition is increasedby 60° C. The base parameter of this plot is O2/C is equal to about0.52, and S/C is equal to about 1.65.

The inventors have found that the oxygen to carbon ratio also effectsthe ignition temperature. FIG. 10 shows how increasing the ratiodecreased the light off temperature.

Keeping the total flow-rate constant, the O₂/C was varied to investigatethe effect on ignition temperature. The S/C remained fixed at 1.65. FIG.10 shows the effect of ignition temperature as function of O₂/C at 14 or20 SLPM (50 percent and 70 percent rated flow). Increasing O₂/Cdecreases the inlet temperature needed to sustain oxidation reactionswithin the hexa-aluminate catalyst. At 50 percent rated flow, increasingthe O₂/C from 0.4 to 0.55 decreases the inlet temperature by almost 80°C. for light-off. A similar behavior is observed at higher-flow rates,although the slope seems to decrease somewhat as flow-rate increases.

As the O₂/C ratio increased, the peak temperature on the Rh-catalystincreased when oxygen was consumed primarily within the Rh-catalyst. Thepeak temperature in that segment increased as the O₂/C ratio increasedand vice versa. As the temperature in the Rh-increases, more heat isconducted back to the hexa-aluminate and less pre-heat is needed for theinlet reactants to ignite and sustain the oxidation reactions in thehexa-aluminate.

FIG. 11 is a graph depicting the relationship between light offtemperature of the system and the steam:carbon molar ratio.

The flow rate and oxygen-to-carbon ratio (O2/C) were kept constant at 14SLPM (50 percent rated flow rate) and 0.52 respectively while varyingthe S/C ratio from 1.65 to 3. As shown in FIG. 11, the increased steamcontent increases the inlet temperature needed to sustain oxidationreactions within the hexa-aluminate catalyst. The inlet temperatureincreases by about 90° C. for light-off when the S/C ratio is changedfrom 1.65 to 3. This effect is to be expected, as higher steam contentin the inlet feed mixture tends to reduce the temperature within thecatalyst. This occurs from two factors a) an increased S/C ratio mayincrease the endothermic steam reforming reactions and b) increasing theS/C ratio reduces the concentration of fuel and air mixture thusdiluting the reactants.

By the time the partially oxidized fluid contacts the Rh-Catalystportion of the system, the temperatures have dissipated to approximately800° C., and further decrease to approximately 700° C. with nodetrimental effect to the efficiency of the reforming process. As such,in an embodiment of the invented system, completion of the reformingprocess by the downstream noble metal-containing catalyst occurs at aslow as 700 C, and usually between 700 C and 850 C.

Table 1, below provides parameters determined empirically, to achieveminimum inlet temperatures of methane fuel feed to assure light off whenhexa-aluminate oxidation catalyst and rhodium-based catalyst isutilized. The parameters include molar fractions of reactants, feed flowrates, and feed velocities. The catalyst structure used in theseexperiments was foam.

TABLE 1 Parameters for achieving targeted minimum inlet fueltemperatures. O₂ molar fraction in Feed, % 10.14 10.14 10.44 8.78 8.038.03 CH₄ molar fraction in Feed, % 19.51 19.51 18.98 21.96 15.44 15.44H₂O molar fraction in Feed, % 32.2 32.2 31.3 36.2 46.3 25.4 O₂/CH₄ inFeed 0.52 0.52 0.55 0.40 0.52 0.52 H₂O/CH₄ in Feed 1.65 1.65 1.65 1.653.0 1.65 Feed Flow Rate, SLPM 28.2 14.1 14.1 14.1 14.1 14.1 SuperficialVelocity, cm/s 41.2 20.6 20.6 20.6 20.6 20.6 (at 25° C.) Min.Temperature, ° C. 540 480 470 539 560 530

Generally, oxygen molar fractions in the feed can vary from 7 to 12percent. Fuel molar fractions, such as methane, can vary from 14 to 20percent. Water molar fractions can vary from 24 to 50 percent. Oxygen tofuel feed ratios can vary from 0.35 to 0.60. Water to fuel ratios canvary from 1.5 to 3.5 Feed Flow Rates (in SLPM) can vary from 13 to 43cm/s.

Aside from the aforementioned operating ranges and additional, specificparameters empirically determined, can be found at Adachi et al.,Journal of Power Sources 188 (2009) 244-255, the entirety of which isincorporated herein by reference.

Although exemplary implementations of the invention have been depictedand described in detail herein, it will be apparent to those skilled inthe relevant art that various modifications, additions, substitutions,and the like can be made without departing from the spirit of theinvention and these are therefore considered to be within the scope ofthe invention as defined in the following claims.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its scope. While the dimensions and types ofmaterials described herein are intended to define the parameters of theinvention, they are by no means limiting, but are instead are exemplaryembodiments. Many other embodiments will be apparent to those of skillin the art upon reviewing the above description. The scope of theinvention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the terms“comprising” and “wherein.” Moreover, in the following claims, the terms“first,” “second,” and “third,” are used merely as labels, and are notintended to impose numerical requirements on their objects. Further, thelimitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. §112, sixth paragraph, unless and until such claimlimitations expressly use the phrase “means for” followed by a statementof function void of further structure.

1. A fuel processor comprising: a. a structure adapted to have fluidpass through substantially its entire length, the structure having anupstream portion and a downstream portion; b. a first catalyst supportedat the upstream portion; c. a second catalyst supported at thedownstream portion, wherein the first catalyst is in fluid communicationwith the second catalyst, and d. uncoated foam positioned upstream fromthe first catalyst such that the first catalyst resides between the foamand the second catalyst.
 2. The fuel process as recited in claim 1further comprising a fuel inlet in thermal communication with saidupstream portion.
 3. The fuel processor as recited in claim 1 whereinsaid first catalyst operates at a higher temperature than the secondcatalyst.
 4. The fuel processor as recited in claim 1 wherein said firstcatalyst is an oxidation catalyst and said second catalyst is areforming catalyst.
 5. The fuel processor as recited in claim 1 whereinthe first catalyst and the second catalyst are supported on onecontiguous substrate.
 6. The fuel processor as recited in claim 5wherein the flow structure is a metallic foam defining channelsextending throughout the substrate so as to facilitate fluid exchangefrom an exterior of the substrate to an interior of the substrate. 7.The fuel processor as recited in claim 5 wherein the substrate defineschannels which extend from an upstream end of the substrate to adownstream end of the substrate.
 8. The fuel processor as recited inclaim 1 wherein an ignition source ignites the fuel at an upstreamportion of the substrate.
 9. The fuel processor as recited in claim 1wherein the upstream portion of the structure has a greater diameterthan the downstream portion.
 10. A method for reforming flowing fuel,the method comprising: a. contacting the fuel to an oxidation catalystso as to partially oxidize the fuel and generate heat; b. warming thepartially oxided fuel with the heat while simultaneously warming areforming catalyst with the heat; and c. reacting the partially oxidizedfuel with steam using the reforming catalyst.
 11. The method as recitedin claim 10 wherein the fuel is a fluid selected from the groupconsisting of petroleum-derived fuel, bio-derived fuel, synthetic fuel,and combinations thereof.
 12. The method as recited in claim 10 whereinthe oxidation catalyst and the reforming catalyst are supported on asingle contiguous substrate.
 13. The method as recited in claim 12wherein the substrate defines means for facilitating fluid flowthroughout the volume of the substrate and from an exterior to aninterior of the substrate.
 14. The method as recited in claim 12 whereinthe substrate is a linear flow structure selected from the groupconsisting of cordierite, iron chromium aluminum alloy, mullite,alumina, aluminum titanate, and combinations thereof.
 15. The method asrecited in claim 11 wherein the oxidation catalyst reaches a temperatureof at least 850° C. and the reforming catalyst reaches a temperature ofno more than 850° C.
 16. The method as recited in claim 10 wherein theoxidation catalyst and the reforming catalyst are supported on differentsubstrates.
 17. The method as recited in claim 10 further comprisingdirecting the heat in a backwards flow direction from the oxidationcatalyst and in a forward flow direction from the oxidation catalyst.18. The method as recited in claim 10 further comprising directing theheat from the oxidation catalyst and towards uncoated foam which islarger in volume than the volume of the reforming catalyst.
 19. Themethod as recited in claim 10 wherein the method attains a peaktemperature and the peak temperature is confined to the oxidationcatalyst.